It is known from the prior art to attach car body parts together, by for example, riveting or spot welding them together and more recently laser. A recent trend in the car industry is to use a modular construction for vehicles, whereby individual modules are connected/attached/bonded to form the main vehicle body and associated parts. Typically car door or body panels are welded and/or riveted together in order to achieve a tight attachment of the two parts. Welding uses intense heat to melt one or more of the interfaces of the parts and needs to be performed by specialists aware of the risks of intense heat, both to themselves and to car parts. The intense heat can cause the substrate surface to buckle or melt and great skill is required to ensure that only the sections/portions/spots needing to be welded actually receive the heat so as to minimise the potential for heat damage to other parts. In order to detach these riveted/welded parts strong mechanical strength is required.
It is also known in the prior art to use adhesive compositions to effect secure attachment of two surfaces/substrates of vehicle components. Adhesive compositions or glues have been widely used to secure windscreens to frames by applying the adhesive to one or both surfaces of the components and aligning them so that the surfaces are bonded/attached together. Typically the adhesive compositions contain curing agents in order to promote or accelerate the adhesive solidification process. The curing agents can be heat or moisture activated and are included in the composition so as to cross-link or polymerise the liquid adhesive into solid form and so accelerate the chemical bonding process. In order to detach the adhesive bonded component(s) thermo-mechanical strength can be applied to separate them. For example, in the instance of detaching a windscreen from a frame which has been firmly bonded in place as the adhesive sealant is hardened, typically involves the automotive glass fitter to remove the windscreen (usually in intact form) using a device comprising a cheese-wire or special knives to cut/saw through the hardened rubber along the periphery of the windscreen. This process requires strong physical force to separate structurally the cohesion strength of adhesive and can lead to musculo-skeletal conditions in the fitters themselves as a result of repetitive strain injury. Further problems associated with this method are that the cheese-wires can overheat due to friction, additionally the wires themselves can break. It is becoming routine in the automotive industry in an effort to minimise vehicle weight to improve performance and to reduce petrol consumption to employ adhesives to bond other car components such as door skins to frames, accordingly the use of adhesive compositions is becoming more widespread in this area of technology. In addition as the new End of Life Vehicle (ELV) Directive becomes implemented, there is a need for detachment or debonding of adhesives in the automotive industry so as to dismantle and recycle car parts such as bonded glazing, panels and so on in a quick, cost-effective, safe and if possible reusable way. Thus there is a need for improvements to debonding various surfaces.
Thermally expandable thermoplastic microspheres have been commercially produced for several years and have been used as fillers in polymers, paints, putty, plastisols, printing inks and as fillers in paper, paperboard and explosives. WO 95/24441 describes a substitute to polyurethane foams in the form of an adhesive composition for filling vehicle box parts and providing sound-proofing which includes 5-15% of expandable micro-spheres encapsulating alkanes. WO 00/75254 also describes adhesive and adhesive primer compositions comprising thermo-expandable microspheres, heat activation of the microcapsules creates a pressure along the interfaces of where the composition has been applied which reduces the surface adhesive bonding and shear or tear stress of the adhesive material. The reduction in chemical and/or physical bonding of the adhesion at the interface of the two bonded surfaces is due to the effect of the expanded microspheres so that they may be described as capable of de-bonding with no cohesive fracture when in their expanded state. The microspheres present at the interface change the structure of the bonding adhesive surface to create instant debonding when supplied with the appropriate trigger. The debonding surface energy is approximately one third lower than the cohesive fracture energy.
One of the problems associated with the automotive industry is that at the vehicle end of life (ELV) most of the vehicle components more than 85% have to be detached and removed from the vehicle so that they can be safely disposed of or recycled in separate and dedicated processes. The disposal of vehicles at the end of life can be time consuming, hazardous to health and the environment and expensive as interior items, dashboards, panels, door skins, plates, frames, light units and other such components need to be detached from one another.
A method and apparatus to carry out a method which would enable rapid, ideally in a matter of minutes, non-toxic material degradation in an efficient manner and safe detachment of such components would offer immediate advantage to the prior art, not only in the automotive industry but in any field where it is desired to detach two surfaces/substrates that have been adhered (bonded together) by means of an adhesive bonding system that can be present in either an adhesive and/or primer and/or cleaner component of the system.
It is envisaged that the method of the present invention may be used in many diverse areas where microspheres are used, for example and without limitation, in cleaning and hygiene, dentistry, surgical medicine, sports equipment manufacture, furniture and finishings especially decorative wallpaper and other situations where it is desired to detach more than one surface. The increased volume of expanded microspheres may also be used to aid transport and dispersion of agents deposited on their surface so mitigating the problem of clustering and agents responsible for clustering a phenomenon associated with decreased functional activity.